Method of fabricating smooth seed layers with uniform crystalline texture for high perpendicular magnetic anisotropy materials

ABSTRACT

A method for fabricating a perpendicular magnetic tunnel junction (pMTJ) device includes growing a seed layer on a first electrode of the pMTJ device. The seed layer has a uniform predetermined crystal orientation along a growth axis. The method also includes planarizing the seed layer while maintaining the uniform predetermined crystal orientation of the seed layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/334,015, filed on Jul. 17, 2014, which issued as U.S. Pat. No.9,385,309 on Jul. 5, 2016, in the names of Matthias Georg Gottwald etal., which claims the benefit of U.S. Provisional Patent ApplicationNos. 61/985,444 filed on Apr. 28, 2014, in the names of Matthias GeorgGottwald et al., and 61/986,059 filed on Apr. 29, 2014, in the names ofMatthias Georg Gottwald et al., the disclosures of which are expresslyincorporated by reference herein in their entireties.

TECHNICAL FIELD

The present disclosure generally relates to magnetic tunnel junction(MTJ) devices. More specifically, the present disclosure relates touniform predetermined crystal orientation seed layers for highperpendicular magnetic anisotropy materials.

BACKGROUND

Unlike conventional random access memory (RAM) chip technologies, datais stored by magnetization of storage elements in magnetic RAM (MRAM).The basic structure of the storage elements consists of metallicferromagnetic layers separated by a thin tunneling barrier. Typically,the ferromagnetic layers underneath the barrier (e.g., the pinned layer)have a magnetization that is fixed in a particular direction. Theferromagnetic magnetic layers above the tunneling barrier (e.g., thefree layer) have a magnetization direction that may be altered torepresent either a “1” or a “0.” For example, a “1” may be representedwhen the free layer magnetization is anti-parallel to the fixed layermagnetization. In addition, a “0” may be represented when the free layermagnetization is parallel to the fixed layer magnetization or viceversa. One such device having a fixed layer, a tunneling layer, and afree layer is a magnetic tunnel junction (MTJ). The electricalresistance of an MTJ depends on whether the free layer magnetization andfixed layer magnetization are parallel or anti-parallel to each other. Amemory device such as MRAM is built from an array of individuallyaddressable MTJs.

To write data in a conventional MRAM, a write current, which exceeds acritical switching current, is applied through an MTJ. Application of awrite current that exceeds the critical switching current changes themagnetization direction of the free layer. When the write current flowsin a first direction, the MTJ may be placed into or remain in a firststate in which its free layer magnetization direction and fixed layermagnetization direction are aligned in a parallel orientation. When thewrite current flows in a second direction, opposite to the firstdirection, the MTJ may be placed into or remain in a second state inwhich its free layer magnetization and fixed layer magnetization are inan anti-parallel orientation.

To read data in a conventional MRAM, a read current may flow through theMTJ via the same current path used to write data in the MTJ. If themagnetizations of the MTJ's free layer and fixed layer are orientedparallel to each other, the MTJ presents a parallel resistance. Theparallel resistance is different than a resistance (anti-parallel) theMTJ would present if the magnetizations of the free layer and the fixedlayer were in an anti-parallel orientation. In a conventional MRAM, twodistinct states are defined by these two different resistances of an MTJin a bitcell of the MRAM. The two different resistances indicate whethera logic “0” or a logic “1” value is stored by the MTJ.

SUMMARY

A method of fabricating a perpendicular magnetic tunnel junction (pMTJ)device includes growing a seed layer on a first electrode of the pMTJdevice. The seed layer has a uniform predetermined crystal orientationalong a growth axis. The method also includes planarizing the seed layerwhile maintaining the uniform predetermined crystal orientation of theseed layer.

A pMTJ device includes a seed layer on a first electrode of the pMTJdevice. The seed layer has a uniform predetermined crystal orientationalong a growth axis and a substantially planar surface. The pMTJ devicealso includes a magnetic material on the substantially planar surface ofthe seed layer.

A pMTJ device includes a seed layer on a first electrode of the pMTJdevice. The seed layer has a uniform predetermined crystal orientationat least along its growth axis and a substantially planar surface. ThepMTJ device also includes means for generating magnetic charge on thesubstantially planar surface of the seed layer.

This has outlined, rather broadly, the features and technical advantagesof the present disclosure in order that the detailed description thatfollows may be better understood. Additional features and advantages ofthe disclosure will be described below. It should be appreciated bythose skilled in the art that this disclosure may be readily utilized asa basis for modifying or designing other structures for carrying out thesame purposes of the present disclosure. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the teachings of the disclosure as set forth in the appendedclaims. The novel features, which are believed to be characteristic ofthe disclosure, both as to its organization and method of operation,together with further objects and advantages, will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following description taken in conjunction with theaccompanying drawings.

FIG. 1 is a diagram of a magnetic tunnel junction (MTJ) device connectedto an access transistor.

FIG. 2 is a conceptual diagram of a conventional magnetic random accessmemory (MRAM) cell including an MTJ.

FIG. 3 is a schematic cross-sectional view of a perpendicular magnetictunnel junction (pMTJ) structure according to aspects of the presentdisclosure.

FIGS. 4A-4C are schematic cross-sectional views of a pMTJ structureillustrating a seed layer manufacturing process according to aspects ofthe present disclosure.

FIGS. 5A-5B are schematic cross-sectional views of pMTJ structuresfabricated with a conventional seed layer manufacturing process versus aseed layer manufacturing process according to aspects of the presentdisclosure.

FIG. 6 is a process flow diagram illustrating a method of fabricating apMTJ device according to aspects of the present disclosure.

FIG. 7 is a block diagram showing an exemplary wireless communicationsystem in which a configuration of the disclosure may be advantageouslyemployed.

FIG. 8 is a block diagram illustrating a design workstation used forcircuit, layout, and logic design of a semiconductor component accordingto one configuration.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. It will be apparent,however, to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts. As described herein, the use of the term“and/or” is intended to represent an “inclusive OR”, and the use of theterm “or” is intended to represent an “exclusive OR”.

MRAM is a non-volatile memory technology that uses magnetic elements.For example, spin transfer torque magnetoresistive random access memory(STT-MRAM) uses electrons that become spin-polarized as the electronspass through a thin film (spin filter). STT-MRAM is also known as spintransfer torque RAM (STT-RAM), spin torque transfer magnetizationswitching RAM (Spin-RAM), and spin momentum transfer (SMT-RAM).

Bitcells of a magnetic random access memory may be arranged in one ormore arrays including a pattern of memory elements (e.g., MTJs in caseof MRAM). Spin-transfer-torque magnetic random access memory (STT-MRAM)is an emerging nonvolatile memory that has advantages of non-volatility.In particular, STT-MRAM operates at a higher speed than off chip dynamicrandom access memory (DRAM). In addition, STT-MRAM has a smaller chipsize than embedded static random access memory (eSRAM), unlimitedread/write endurance, and a low array leakage current.

Perpendicular magnetic tunnel junctions (pMTJs) may be elements withinSTT-MRAMs. Devices such as pMTJs, however, specify the use of highperpendicular magnetic anisotropy (PMA) materials, which can be used asreference layers. The use of perpendicular magnetic multilayerscontaining only 3d magnetic elements is considered beneficial, where 3drefers to the position of the chemical element in the periodic table(e.g., elements 21-30). Examples of magnetic multilayers containing 3dmagnetic elements that may be used as high PMA materials include cobaltnickel (Co/Ni) or cobalt iron/nickel (CoFe/Ni)). In particular, the useof 3d elements may be beneficial from the point of view of thepatterning process because their usage improves the effectiveness ofreactive ion etching (RIE) and the spin transfer torque efficiency.These materials, which may include a ten (10) to (20) nanometer thicknickel chromium (NiCr) alloy, may also specify crystalline seed layersthat provide a high texture and a small lattice mismatch. Unfortunately,the crystallinity of the seed layers may lead to a degree of roughness(e.g., greater than 0.5 nanometers). This degree of roughness may beincompatible with obtaining the high magnetoresistive performance of,for example, a magnesium oxide (MgO) based tunneling device or otherMRAM-based devices.

One aspect of the disclosure includes a two-step approach to manufactureseed layers with high crystalline textures for perpendicular magneticmaterial elements (e.g., a NiCr-alloy seed layer for a [CoFe/Ni]multilayer). This two-step approach also fulfills the topologicalspecifications of high performance MgO-based pMTJs. The first step mayinclude growing a seed layer on a first electrode of the pMTJ, in whichthe seed layer has a uniform and predetermined crystal orientation alonga growth axis of the seed layer. The second step may include planarizingthe seed layer while maintaining the uniform, predetermined crystalorientation along the growth direction, or the direction of the growthaxis of the seed layer. Etching processes such as chemical mechanicalpolishing (CMP) may be employed to planarize the seed layer. Forexample, CMP can planarize the seed layer to a predetermined smoothnessof a root mean square (RMS) below 0.2 nanometers without changing thecrystalline texture (i.e., the crystalline orientation along the growthaxis) of a device. An initial thickness of the seed layer may betwenty-five (25) to thirty (30) nanometers. The thickness of the seedlayer following planarization may be in the range of ten (10) to twenty(20) nanometers. The uniform, predetermined crystal orientation alongthe growth direction of the seed layer may be a (111) crystalorientation, for example.

FIG. 1 illustrates a memory cell 100 of a memory device including amagnetic tunnel junction (MTJ) 102 coupled to an access transistor 104.The memory device may be a magnetic random access memory (MRAM) devicethat is built from an array of individually addressable MTJs. An MTJstack may include a free layer, a fixed layer and a tunnel barrier layerthere between as well as one or more ferromagnetic layers.Representatively, a free layer 110 of the MTJ 102 is coupled to a bitline 112. The access transistor 104 is coupled between a fixed layer 106of the MTJ 102 and a fixed potential node 122. A tunnel barrier layer114 is coupled between the fixed layer 106 and the free layer 110. Theaccess transistor 104 includes a gate 116 coupled to a word line 118.

Synthetic anti-ferromagnetic materials may be used to form the fixedlayer 106 and the free layer 110. For example, the fixed layer 106 maycomprise multiple material layers including a cobalt-iron-boron (CoFeB)layer, a ruthenium (Ru) layer and a cobalt-iron (CoFe) layer. Inaddition, the free layer 110 may also include multiple material layersincluding a cobalt-iron-boron (CoFeB) layer, a ruthenium (Ru) layer anda cobalt-iron (CoFe) layer. In addition, the tunnel barrier layer 114may be magnesium oxide (MgO).

FIG. 2 illustrates a conventional STT-MRAM bit cell 200. The STT-MRAMbit cell 200 includes a magnetic tunnel junction (MTJ) storage element205, a transistor 201, a bit line 202 and a word line 203. The MTJstorage element is formed, for example, from at least two ferromagneticlayers (a pinned layer and a free layer), each of which can hold amagnetic field or polarization, separated by a thin non-magneticinsulating layer (tunneling barrier). Electrons from the twoferromagnetic layers can penetrate through the tunneling barrier due toa tunneling effect under a bias voltage applied to the ferromagneticlayers. The magnetic polarization of the free layer can be reversed sothat the polarity of the pinned layer and the free layer are eithersubstantially aligned or opposite. The resistance of the electrical paththrough the MTJ varies depending on the alignment of the polarizationsof the pinned and free layers. This variance in resistance may be usedto program and read the bit cell 200. The STT-MRAM bit cell 200 alsoincludes a source line 204, a sense amplifier 208, read/write circuitry206 and a bit line reference 207.

The crystalline orientation along the growth axis (e.g., the texture)should be uniform between the seed layer and the high perpendicularmagnetic anisotropy (PMA) material. The texture may be measured in amaterial by using x-ray diffraction. As described herein, the terms“high” or “good” texture may be uniform crystalline orientation alongthe growth axis of the seed layer. High PMA may also occur in conditionsthat are the opposite to magnetostatics. For example, in thin filmshaving a thickness smaller than lateral dimensions, a magnetostaticdemagnetizing field may favor in-plane magnetization.

If strong PMA is desired for the magnetic material, a mechanism within acrystalline structure is specified to break the crystalline symmetryperpendicular to the plane. That is, some sort of “symmetry breaking”force or other mechanism is provided in the crystalline structure. Inaddition, the magnetic material may be crystalline. As a result, thismagnetic material may exhibit a special crystalline axis in which themagnetization prefers to be directed, referred to herein as an “easyaxis.” Therefore, if strong PMA is desired, the direction of crystalgrowth, or the growth axis, extends in the same direction as thedirection in which the easy axis points.

The direction of the crystal growth is not only important for providingstrong PMA in the magnetic crystalline material, but also for providingstrong PMA at an interface of a crystalline material. For example,cobalt nickel interfaces would apply. Important properties to examinewould be the growth direction of a given crystal, and whether or not theinterface anisotropy or interface PMA of a crystalline material is highor low for that specific growth direction. For example, in the case ofcobalt nickel, the (111) crystal orientation direction achieves thehighest PMA from the crystalline point of view and also from theinterface anisotropy point of view. That is why it is important thatcobalt nickel or cobalt iron nickel grow along the (111) crystalorientation axis.

FIG. 3 is a schematic cross-sectional view of a perpendicular magnetictunnel junction (pMTJ) structure 300 according to aspects of the presentdisclosure. The pMTJ structure 300 (e.g., pMTJ device) includes a firstelectrode 302, a seed layer 304, a high perpendicular magneticanisotropy (PMA) layer 306, and a texture breaking layer 308. The pMTJstructure 300 also includes a cobalt (C) iron (Fe) and boron (B) (CFB)based spin-polarizing layer 310, a tunneling barrier 312, a free layer314, and a second electrode 316.

The seed layer 304 on the first electrode 302 may have a uniformpredetermined crystal orientation along a growth axis of the seed layer304, as well as a substantially planar surface of the seed layer 304.The texture of the seed layer may refer to the degree of crystallineorder in a material, or how well-crystallized a given material is,within a particular crystal orientation or direction of interest. In oneconfiguration, the uniform predetermined crystal orientation along thegrowth axis of the seed layer is a (111) crystal orientation. The highPMA layer 306 may be a magnetic material on the substantially planarsurface of the seed layer 304. The seed layer 304 may be planarized to athickness in the range of 10 (ten) to 20 (twenty) nanometers to providea predetermined smoothness.

According to an aspect of the present disclosure, the smoothness of asurface of a crystalline structure is a property that occurs togetherwith the crystalline orientation of that crystalline structure along agrowth axis. The smoothness of a crystalline structure may be a rootmean square (RMS) below 0.2 nanometers without changing the crystallinetexture or the crystalline orientation along the growth axis. Forexample, the above-described smoothness may be specified for a materialwith a thickness in the range of 10 (ten) to 20 (twenty) nanometers.This exemplary thickness range is a thickness range in which chemicalmechanical polishing (CMP) is feasible. By contrast, other conventionalsmoothness techniques (e.g., plasma smoothing treatment) may only beapplicable to thicknesses of much smaller magnitudes, or differentsmoothing treatments, which may only be applicable to thicknesses ofmuch larger magnitudes.

The first electrode 302 and the second electrode 316 can be anyconductive material such as copper or aluminum. The seed layer 304 maybe made of, or include, nickel chromium (NiCr), hafnium (Hf), ruthenium(Ru), a platinum (Pt) alloy or multilayer, or similar materials thathave high texture and small lattice mismatch that may also have highcrystallinity. The high PMA layer 306 may be made of multilayers thatare based on a precious conductive material such as palladium orplatinum with cobalt, or can be made of 3d metal multilayers that arebased on a transition-conductive material like cobalt nickel or cobaltiron nickel. The texture breaking layer 308 may be tantalum, iron,and/or iron tantalum, and is usually inserted between the high PMA layer306 and the CFB based spin-polarizing layer 310. The CFB basedspin-polarizing layer 310 can be cobalt, iron and/or boron. Thetunneling barrier 312 may be a magnesium oxide (MgO). For an MTJ, thetunneling barrier 312 may function as the MTJ's barrier layer. Thereference layer or the fixed layer includes the materials between thefirst electrode 302 and a surface of the tunneling barrier 312.

The specification for a high PMA material and seed layer combination ina pMTJ structure may include a magnesium oxide (MgO) compatibletopology, a compatible reactive ion etching (RIE) chemistry forpatterning, and an overall structure that is compatible with a high spintransfer torque (STT) efficiency. Fabricating the pMTJ structure isperformed to provide a high performance device with well-adaptedcrystallinity in the structure. The crystallinity in the structureenables desired magnetic properties for perpendicular materials, whichmay be based on 3d transition metals such as cobalt or nickel multilayermetallic structures.

A tradeoff occurs between the thickness of the seed layer 304 and thetexture when the seed layer 304 is built. For example, if the seed layer304 is too thin, then the degree of texture is poor. On the other hand,when the seed layer 304 is too thick, the seed layer exhibits a veryrough surface. The seed layer 304 should have an increased thickness anda high texture. In addition, the surface of the seed layer 304 should berelatively smooth. Processes such as chemical mechanical polishing (CMP)can smooth the surface of the seed layer 304 to a degree of a fewnanometers, for example. Some seed layers with smooth surfaces may alsostill have high-density textures because some crystalline materialalready exists in such seed layers.

In one configuration, the seed layer 304 has an increased thickness anda predetermined smoothness. In this configuration, the predeterminedsmoothness may be a root means square (RMS) less than 0.2 nanometers. Inthis configuration, the pMTJs (e.g., MTJ stacks) have a seed layer 304that provides a number of performance advantages, including ease inpatterning, high spin torque transfer efficiency, more efficient use ofmanufacturing materials, more precise device alignment, and lower devicedependability for smaller device distributions. By having smoother seedlayers and/or other layers, the effective interfaces between layers arealso maintained, which improves the overall device performance.

In this configuration, the seed layer 304 is smoothed using CMP toprovide a high crystalline smoothness that is specified for a surface318 of the CFB based spin-polarizing layer 310. Roughness in the seedlayer 304 prohibits the surface 318 of the CFB based spin-polarizinglayer 310 in having a desired smoothness. The adapted crystallinitylevel 320 specifies an adapted crystallinity of the seed layer 304 andthe high PMA layer 306, which is smoothed to achieve the highcrystalline smoothness that is specified for the surface 318 of the CFBbased spin-polarizing layer 310 and the tunneling barrier 312. Adaptedcrystallinity can be defined as a crystalline orientation thatsubstantially increases the perpendicular part of the magneticcrystalline anisotropies and the magnetic interface anisotropies of thehigh PMA material.

A pMTJ manufacturing process, according to one aspect of the presentdisclosure, obtains both good performance and a good texture in the seedlayer 304. For example, using CMP on the seed layer 304 provides bothgood texture and good performance. CMP on the seed layer 304, however,may contaminate the seed layer 304. According to one aspect of thepresent disclosure, any contamination or by-products of contamination inthe seed layer 304 may be removed by processes such as pre-sputtering ormild etching.

FIGS. 4A-4C are schematic cross-sectional views of a pMTJ structureillustrating a seed layer manufacturing process according to aspects ofthe present disclosure.

FIG. 4A shows a pMTJ structure 400 with a first electrode 402 and arough seed layer 404. The rough seed layer 404 contains high texture aswell as high roughness. FIG. 4A shows when the rough seed layer 404 isfirst deposited on the first electrode 402. In one configuration, around25-30 nm of rough seed layer material is deposited on the firstelectrode 402. In one configuration, the rough seed layer 404 is amaterial including nickel chromium (NiCr), hafnium (Hf), ruthenium (Ru)or a platinum (Pt) alloy or multilayer.

FIG. 4B shows a pMTJ structure 410 with the first electrode 402 and asmoothed seed layer 406. The smoothed seed layer 406 of the pMTJstructure 410 results from CMP or another smoothing process applied tothe rough seed layer 404 of the pMTJ structure 400 in FIG. 4A. Thesmoothed seed layer 406 has little roughness and is smooth, but stillcontains a high texture. In one configuration, the smoothed seed layer406 is reduced to around 10-20 nm of material with CMP. For CMP, havingto remove large amounts of material is not desired.

FIG. 4C shows a pMTJ structure 420 with the first electrode 402, thesmoothed seed layer 406 and a high perpendicular magnetic anisotropy(PMA) layer 408. The high PMA layer 408 may be smooth or rough whendeposited on the smoothed seed layer 406. The high PMA layer 408 overthe smoothed seed layer 406 results in adapted crystallinity, whichmakes the pMTJ structure 420 a high-performance pMTJ structure. The highPMA layer 408 may also be a cobalt-platinum based material or referencelayer, which can grow well on seed layers made from various materials,and which may also have some advantages for STT-MRAM applications. Theseed layer may also be adapted to a multilayer transition metal layersuch as cobalt nickel, or cobalt iron nickel, for example. In oneconfiguration, platinum or palladium-based layers are avoided in thelayers of a pMTJ structure.

There are two kinds of multilayers that can provide good PMA for use inthe high PMA layer 408, for example. First, there are multilayers basedon a precious conductive material such as palladium or platinum, withcobalt. Second, there are multilayers made from only 3dtransition-conductive materials like cobalt nickel or cobalt ironnickel. From the perspective of STT-MRAM, it is desirable to use 3dtransition conductive material only multilayers. Those 3d-transitionconductive material only multilayers should have very well-adapted seedlayers. An example of such a well-adapted seed layer is e.g., nickelchromium (NiCr). In addition, the well-adapted seed layer should be asthick as possible to obtain good texture and crystallinity. However,roughness problems—such as shown above in FIG. 4A—may occur at the seedlayers. As a result, the present disclosure provides approaches to solveroughness issues and produce smooth seed layers.

FIGS. 5A-5B are schematic cross-sectional views of pMTJ structuresfabricated with a conventional seed layer manufacturing process versus aseed layer manufacturing process according to aspects of the presentdisclosure.

FIG. 5A shows a pMTJ structure 500 with a first electrode 502, a roughseed layer 504, a rough high PMA layer 506, a rough spin polarizinglayer 508, a rough tunneling barrier 512, and a rough free layer 514,which may be carbon-iron (Fe)-boron (CFB) based. A seed layer and highPMA layer region 510 includes the first electrode 502, the rough seedlayer 504 and the rough high PMA layer 506. A tunneling structure withbarrier region 516 includes the rough spin polarizing layer 508, therough tunneling barrier 512 and the rough free layer 514.

FIG. 5B shows a pMTJ structure 500 with a smoothed first electrode 502′,a smoothed seed layer 504′, a smoothed high PMA layer 506′, a smoothedspin polarizing layer 508′, a smoothed tunneling barrier 512′, and asmoothed free layer 514′. A smoothed seed layer and high PMA layerregion 510′ includes the smoothed first electrode 502′, the smoothedseed layer 504′ and the smoothed high PMA layer 506′. A smoothedtunneling structure with barrier region 516′ includes the smoothed spinpolarizing layer 508′, the smoothed tunneling barrier 512′ and thesmoothed free layer 514′. The pMTJ structure 520 results when the roughseed layer 504 of pMTJ structure 500 has undergone a smoothing processsuch as CMP.

In one configuration, the rough spin polarizing layer 508 and thesmoothed spin polarizing layer 508′ correspond to the CFB basedspin-polarizing layer 310 of FIG. 3; the rough tunneling barrier 512 andthe smoothed tunneling barrier 512′ correspond to the tunneling barrier312 of FIG. 3; and the rough free layer 514 and the smoothed free layer514′ correspond to the free layer 314 of FIG. 3.

The smoothed seed layer 504′ (and smoothed seed layer 406 of FIGS.4B-4C) on the first electrode 502 (and the first electrode 402 of FIGS.4A-4C) may have a uniform predetermined crystal orientation at leastalong their respective growth axes as well as a substantially planarsurface. In one configuration, the uniform predetermined crystalorientation along the growth axis is a (111) crystal orientation. Thehigh PMA layer 506′ (and the high PMA layer 408 of FIG. 4C) may be amagnetic material that is on the substantially planar surface of thesmoothed seed layers 504′ and 406.

FIG. 6 is a process flow diagram illustrating a method 600 offabricating a pMTJ device according to aspects of the presentdisclosure. In block 602, a seed layer (e.g., seed layer 304, rough seedlayer 404, rough seed layer 504) is grown on a first electrode (e.g.,first electrode 302, first electrode 402, first electrode 502, smoothedfirst electrode 502′) of a perpendicular magnetic tunnel junction (e.g.,pMTJ structures 300, 400, 410, 420, 500, 520). The seed layer has auniform, predetermined crystal orientation along a growth axis of theseed layer. In block 604, the seed layer is planarized (to become e.g.,the smoothed seed layer 406, smoothed seed layer 504′) while maintainingthe uniform, predetermined crystal orientation of the seed layer along agrowth axis of the seed layer.

In one configuration, the seed layer is etched after planarizing. Inanother configuration, planarizing the seed layer includes chemicalmechanical polishing (CMP) the seed layer, and removing residue from thechemical mechanical polishing of the seed layer to maintain the uniform,predetermined crystalline orientation of the seed layer along a growthaxis of the seed layer.

According to one aspect of the present disclosure, a perpendicularmagnetic tunnel junction (pMTJ) device comprises a seed layer on a firstelectrode of the pMTJ device, the seed layer having a uniformpredetermined crystal orientation along a growth axis and asubstantially planar surface of the seed layer. The pMTJ device alsoincludes means for generating magnetic charge on the substantiallyplanar surface of the seed layer. In one configuration, the magneticcharge generating means is the high PMA layer 306, the high PMA layer408, the rough high PMA layer 506, and/or the smoothed high PMA layer506′. In another configuration, the aforementioned means may be anymaterial or any layer configured to perform the functions recited by theaforementioned means. Although specific means have been set forth, itwill be appreciated by those skilled in the art that not all of thedisclosed means are required to practice the disclosed configurations.Moreover, certain well known means have not been described, to maintainfocus on the disclosure.

In one configuration, the conductive material used for the variousconductive layers including the first electrodes 302, 402, 502, thesmoothed first electrode 502′ and the second electrode 316 are copper(Cu), or other conductive materials with high conductivity.Alternatively, the conductive material may include copper (Cu), silver(Ag), annealed copper (Cu), gold (Au), aluminum (Al), calcium (Ca),tungsten (W), zinc (Zn), nickel (Ni), lithium (Li) or iron (Fe). Theaforementioned conductive material layers may also be deposited byelectroplating, chemical vapor deposition (CVD), physical vapordeposition (PVD), sputtering, or evaporation.

The seed layers (e.g., seed layer 304, rough seed layer 404, rough seedlayer 504, smoothed seed layer 406, smoothed seed layer 504′) may bematerials including nickel chromium (NiCr), hafnium (Hf), ruthenium(Ru), or a platinum (Pt) alloy or multilayer, or an alloy or multilayerof any of the previously listed materials other than platinum.

The high PMA layers 306, 408, 506, and 506′ may include multilayersbased on a precious conductive material such as palladium or platinum,with cobalt, such as cobalt palladium (Co/Pa) or cobalt platinum(Co/Pt), or alloys of any of the previously listed materials. Theaforementioned high PMA layers may also include multilayers made fromonly 3d transition-conductive materials like cobalt nickel (Co/Ni) orcobalt iron/nickel (CoFe/Ni), or alloys of the previously listedmaterials. The 3d refers to an element's position in the periodic table(e.g., elements 21-30).

Any insulating materials used in any of the aforementioned pMTJstructures may be made of materials having a low k, or a low dielectricconstant value, including silicon dioxide (SiO₂) and fluorine-doped,carbon-doped, and porous carbon-doped forms, as well as spin-on organicpolymeric dielectrics such as polyimide, polynorbomenes,benzocyclobutene (BCB) and polytetrafluoroethylene (PTFE), spin-onsilicone based polymeric dielectrics and silicon nitrogen-containingoxycarbides (SiCON).

Although not mentioned in the above process steps, photoresist,ultraviolet exposure through masks, photoresist development andlithography may be used. Photoresist layers may be deposited byspin-coating, droplet-based photoresist deposition, spraying, chemicalvapor deposition (CVD), physical vapor deposition (PVD), sputtering, orevaporation. Photoresist layers may then be exposed and then etched bychemical etching processes using solutions such as Iron Chloride(FeCl₃), Cupric Chloride (CuCl₂) or Alkaline Ammonia (NH₃) to wash awaythe exposed photoresist portions, or dry etching processes usingplasmas. Photoresist layers may also be stripped by a chemicalphotoresist stripping process or a dry photoresist stripping processusing plasmas such as oxygen, which is known as ashing.

FIG. 7 is a block diagram showing an exemplary wireless communicationsystem 700 in which an aspect of the disclosure may be advantageouslyemployed. For purposes of illustration, FIG. 7 shows three remote units720, 730, and 750 and two base stations 740. It will be recognized thatwireless communication systems may have many more remote units and basestations. Remote units 720, 730, and 750 include IC devices 725A, 725Cand 725B that include the disclosed pMTJ device. It will be recognizedthat other devices may also include the disclosed pMTJ device, such asthe base stations, switching devices, and network equipment. FIG. 7shows forward link signals 780 from the base station 740 to the remoteunits 720, 730, and 750 and reverse link signals 790 from the remoteunits 720, 730, and 750 to base stations 740.

In FIG. 7, remote unit 720 is shown as a mobile telephone, remote unit730 is shown as a portable computer, and remote unit 750 is shown as afixed location remote unit in a wireless local loop system. For example,the remote units may be a mobile phone, a hand-held personalcommunication systems (PCS) unit, a portable data unit such as apersonal data assistant, a GPS enabled device, a navigation device, aset top box, a music player, a video player, an entertainment unit, afixed location data unit such as meter reading equipment, or otherdevices that store or retrieve data or computer instructions, orcombinations thereof. Although FIG. 7 illustrates remote units accordingto the teachings of the disclosure, the disclosure is not limited tothese exemplary illustrated units. Aspects of the disclosure may besuitably employed in many devices, which include the disclosed pMTJdevice.

FIG. 8 is a block diagram illustrating a design workstation used forcircuit, layout, and logic design of a semiconductor component, such asthe pMTJ device disclosed above. A design workstation 800 includes ahard disk 801 containing operating system software, support files, anddesign software such as Cadence or OrCAD. The design workstation 800also includes a display 802 to facilitate design of a circuit 810 or asemiconductor component 812 such as a pMTJ device. A storage medium 804is provided for tangibly storing the circuit design 810 or thesemiconductor component 812. The circuit design 810 or the semiconductorcomponent 812 may be stored on the storage medium 804 in a file formatsuch as GDSII or GERBER. The storage medium 804 may be a CD-ROM, DVD,hard disk, flash memory, or other appropriate device. Furthermore, thedesign workstation 800 includes a drive apparatus 803 for acceptinginput from or writing output to the storage medium 804.

Data recorded on the storage medium 804 may include specify logiccircuit configurations, pattern data for photolithography masks, or maskpattern data for serial write tools such as electron beam lithography.The data may further include logic verification data such as timingdiagrams or net circuits associated with logic simulations. Providingdata on the storage medium 804 facilitates the design of the circuitdesign 810 or the semiconductor component 812 by decreasing the numberof processes for designing semiconductor wafers.

For a firmware and/or software implementation, the methodologies may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. A machine-readable mediumtangibly embodying instructions may be used in implementing themethodologies described herein. For example, software codes may bestored in a memory and executed by a processor unit. Memory may beimplemented within the processor unit or external to the processor unit.As used herein, the term “memory” refers to types of long term, shortterm, volatile, nonvolatile, or other memory and is not to be limited toa particular type of memory or number of memories, or type of media uponwhich memory is stored.

If implemented in firmware and/or software, the functions may be storedas one or more instructions or code on a computer-readable medium.Examples include computer-readable media encoded with a data structureand computer-readable media encoded with a computer program.Computer-readable media includes physical computer storage media. Astorage medium may be an available medium that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can include RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, orother medium that can be used to store desired program code in the formof instructions or data structures and that can be accessed by acomputer; disk and disc, as used herein, includes compact disc (CD),laser disc, optical disc, digital versatile disc (DVD), floppy disk andBlu-ray disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers. Combinations of the aboveshould also be included within the scope of computer-readable media.

In addition to storage on computer-readable medium, instructions and/ordata may be provided as signals on transmission media included in acommunication apparatus. For example, a communication apparatus mayinclude a transceiver having signals indicative of instructions anddata. The instructions and data are configured to cause one or moreprocessors to implement the functions outlined in the claims.

The exemplary aspects discussed herein, beneficially allow the MTJ stackto be protected from at least the process related damages describedabove, thereby generating high yield in the fabrication of MTJs. Itshould be appreciated that the various layers of the MTJ stack areprovided merely for illustration and not for limitation. Additionallayers may be added and/or layers may be removed or combined and maycomprise different materials then illustrated.

It should be appreciated that memory devices including the MTJ storageelements described herein may be included within a mobile phone,portable computer, hand-held personal communication system (PCS) unit, aportable data unit such as a personal data assistants (PDA), a GPSenabled device, a navigation device, a set top box, a music player, avideo players, an entertainment unit, a fixed location data unit such asmeter reading equipment, or any other device that stores or retrievesdata or computer instructions, or any combination thereof. Accordingly,aspects of the disclosure may be suitably employed in any device, whichincludes active integrated circuitry including memory having MTJ storageelements as disclosed herein.

Further, it should be appreciated that various to memory devices caninclude an array of MTJ storage elements as disclosed herein.Additionally, the MTJ storage elements disclosed herein may be used invarious other applications, such as in logic circuits. Accordingly,although potions of the foregoing disclosure discuss the stand-alone MTJstorage element, it will be appreciated that various aspects can includedevices into which the MTJ storage element is integrated.

Accordingly, aspects can include machine-readable media orcomputer-readable media embodying instructions which when executed by aprocessor transform the processor and any other cooperating elementsinto a machine for performing the functionalities described herein asprovided for by the instructions.

While the foregoing disclosure shows illustrative aspects, it should benoted that various changes and modifications could be made hereinwithout departing from the scope of the disclosure as defined by theappended claims. The functions, steps and/or actions of the methodclaims in accordance with the aspects described herein need not beperformed in any particular order. Furthermore, although elements of theaspects may be described or claimed in the singular, the plural iscontemplated unless limitation to the singular is explicitly stated.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the technologyof the disclosure as defined by the appended claims. For example,relational terms, such as “above,” “below,” “top” and “bottom” are usedwith respect to a substrate or electronic device. Of course, if thesubstrate or electronic device is inverted, above becomes below, topbecomes bottom and vice versa. Additionally, if oriented sideways, theterms “above,” “below,” “top” and “bottom” may refer to sides of asubstrate or electronic device, for example.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects. Likewise, the term “aspects of the disclosure” does notrequire that all aspects of the disclosure include the discussedfeature, advantage or mode of operation. The terminology used herein isfor the purpose of describing particular aspects only and is notintended to be limiting of aspects of the disclosure.

As used herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Moreover, the scope of the present application is not intended to belimited to the particular configurations of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the correspondingconfigurations described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A method of fabricating a perpendicular magnetictunnel junction (pMTJ) device, comprising: growing a seed layer on afirst electrode of the pMTJ device, the seed layer having a uniformpredetermined crystal orientation at least along a growth axis, in whichthe growth axis is in a same direction as an easy axis; and planarizingthe seed layer while maintaining the uniform predetermined crystalorientation of the seed layer.
 2. The method of claim 1, in which theuniform predetermined crystal orientation of the seed layer comprises a(111) crystal orientation.
 3. The method of claim 1, in whichplanarizing the seed layer comprises achieving a smoothness for the seedlayer comprising a root mean square (RMS) below 0.2 nanometers.
 4. Themethod of claim 3, in which a thickness of the seed layer is in a rangeof ten (10) to twenty (20) nanometers.
 5. The method of claim 1, furthercomprising integrating the pMTJ device into a mobile phone, a set topbox, a music player, a video player, an entertainment unit, a navigationdevice, a computer, a hand-held personal communication systems (PCS)unit, a portable data unit, and/or a fixed location data unit.
 6. Amethod of fabricating a perpendicular magnetic tunnel junction (pMTJ)device, comprising: growing a seed layer on a first electrode of thepMTJ device, the seed layer having a uniform predetermined crystalorientation at least along a growth axis; planarizing the seed layerwhile maintaining the uniform predetermined crystal orientation of theseed layer; and etching the seed layer after planarizing.
 7. The methodof claim 6, in which planarizing the seed layer comprises: chemicalmechanical polishing the seed layer; and removing residue from thechemical mechanical polishing of the seed layer to maintain the uniformpredetermined crystal orientation of the seed layer.
 8. A method offabricating a perpendicular magnetic tunnel junction (pMTJ) device,comprising the steps of: growing a seed layer on a first electrode ofthe pMTJ device, the seed layer having a uniform predetermined crystalorientation at least along a growth axis, in which the growth axis is ina same direction as an easy axis; and planarizing the seed layer whilemaintaining the uniform predetermined crystal orientation of the seedlayer.
 9. The method of claim 8, in which the uniform predeterminedcrystal orientation of the seed layer comprises a (111) crystalorientation.
 10. The method of claim 8, in which planarizing the seedlayer comprises achieving a smoothness for the seed layer comprising aroot mean square (RMS) below 0.2 nanometers.
 11. The method of claim 10,in which a thickness of the seed layer is in a range of ten (10) totwenty (20) nanometers.
 12. The method of claim 8, further comprisingthe step of integrating the pMTJ device into a mobile phone, a set topbox, a music player, a video player, an entertainment unit, a navigationdevice, a computer, a hand-held personal communication systems (PCS)unit, a portable data unit, and/or a fixed location data unit.
 13. Amethod of fabricating a perpendicular magnetic tunnel junction (pMTJ)device, comprising the steps of: growing a seed layer on a firstelectrode of the pMTJ device, the seed layer having a uniformpredetermined crystal orientation at least along a growth axis;planarizing the seed layer while maintaining the uniform predeterminedcrystal orientation of the seed layer; and etching the seed layer afterplanarizing.
 14. The method of claim 13, in which planarizing the seedlayer comprises the steps of: chemical mechanical polishing the seedlayer; and removing residue from the chemical mechanical polishing ofthe seed layer to maintain the uniform predetermined crystal orientationof the seed layer.